1. Field of the Invention
The present invention relates to a hole center detecting apparatus which can be employed when a wire such as a steel cord for reinforcing a rubber part is wound onto a spool which is a member having a hole. Further, the present invention relates to a straightness measuring apparatus for measuring the straightness of a wire such as a steel cord for reinforcing a rubber part automatically. Still further, the present invention relates to a residual torsion measuring apparatus for measuring the residual torsion of a wire such as a steel cord for reinforcing a rubber part automatically.
2. Description of the Related Art
Prior Art 1:
In the working of the prior art for winding a steel cord for reinforcing a rubber part on a spool (as also called a “reel” or “bobbin”) having an insertion hole, the cord is wound on the spool after a worker inserts its leading end into the insertion hole by visually identifying the insertion hole.
For this automation for improving the production yield, it is necessary to detect the center of the insertion hole automatically with high precision. For example, employing an apparatus for detecting the center position of the hole by locating the hole with a CCD camera and by processing the graphic digital signals with a computer to extract the shape of the hole and to detect the center position of the hole, is conceivable.
However, since this apparatus employs a CCD camera it is disadvantageous in that the total cost is high. In order to eliminate this disadvantage, it is also conceivable to employ a reflection or transparent type optical sensor which has a lower cost than the CCD camera, and thereby to detect the hole directly. However, it is difficult for this apparatus to detect the center position of the hole with high precision.
Prior Art 2:
In the prior art, the curvature (or straightness) per unit length of the steel cord for reinforcing a rubber part such as a steel cord to be used in a pneumatic tire is controlled so as to ensure workability in the tire manufacturing process. Thus at the final step of the steel cord manufacturing process, the straightness is inspected visually by the inspector using an inspection plate.
However, the visual inspection by the inspector involves problems with respect to precision and deterioration in productivity due to the time required for the inspection.
Prior Art 3:
In the steel cord for reinforcing a rubber part of the prior art such as the steel cord to be used in the pneumatic tire, the residual torsion per unit length is specified in order to ensure the workability in the tire manufacturing process. At the final step of the steel cord manufacturing process, therefore, the residual torsion is measured by an inspector having technical ability at or above a predetermined level, and its value is recorded on a check sheet. When the residual torsion is measured, however, the end portion of an object to be measured is bent. Therefore, there may be some variation in the measurement by the inspector of the length or the angle of the same cord when the end portion is bent. This causes some amount of variation with respect to the precision of the residual torsion measurement.
Measurement and inspection of residual torsion in steel cord manufacturing is essential for ensuring workability in tire manufacturing. At the final step of the steel cord manufacturing process, therefore, the residual torsion is measured and inspected exclusively by an inspector who is qualified by a technical institution and thereby has technical ability that is at or above a predetermined level. However, because the residual torsion is always measured at the final step, the productivity tends to deteriorate. In order to maintain precision in the residual torsion measurement, it was necessary to spend a long time training the inspectors to make them qualified, and it was also necessary to check the precision of their measurements periodically even after they became qualified.
Moreover, the residual torsion may be read in either the “plus” or “minus” direction, depending on the kind of steel cord or test standards (e.g., JIS or ASTM) of the steel cord. Therefore, the inspector has to record the direction of the residual torsion according to the kind of the steel cord or the test standards used by the tire manufacturing factory. Therefore, even a qualified inspector may erroneously record the wrong “plus” and “minus” directions for the different steel cord kinds or test standards.